kmap(9)

📦 version 7.3.1, in nixpkgs unstable

💖 kmap(9) — the Kernel API Manual, bestie edition 💖

okay so welcome to kmap(9), straight out of the Kernel API Manual, and no cap this is one of those little functions that has a bigger personality than it looks 💅

✨ NAME ✨

kmap — map a page for long term usage 🗺️✨

🌸 SYNOPSIS 🌸

void * kmap (struct page *page );

🎀 ARGUMENTS 🎀

  • page — pointer to the page that's getting mapped 🫶

⭐ RETURN ⭐

it hands you back the virtual address of the mapping, periodt ✨

🦋 DESCRIPTION 🦋

so here's the vibe check 👑 — you can only invoke this from preemptible task context. why? because on 32bit systems with CONFIG_HIGHMEM enabled, this function might sleep 😴😭. like, it will literally nap on you. so don't be that girl calling it from somewhere that can't handle a snooze.

for systems with CONFIG_HIGHMEM=n, and also for pages sitting in the low memory area, it just returns the virtual address of the direct kernel mapping 🎯 easy, clean, slay.

the returned virtual address is globally visible and stays valid right up to the point where it gets unmapped via kunmap 🔓. and yes bestie, the pointer can be handed off to other contexts — it's not a one-context-only situation, it's main character energy that travels 🌈.

now the ⚠️ moment: for highmem pages on 32bit systems this can be slow 😬 because the mapping space is limited and protected by a global lock 🔒. and if there's no mapping slot available? the function blocks until a slot gets released via kunmap 🧚 it's giving "waiting in line at the club" energy fr fr.

👀 SEE ALSO 👀

kernel file ./include/linux/highmem.h 💫 and all these icons:

🫶 friendly reminder bestie: preemptible task context only. she might sleep. do not test her.

and that's the whole page, no notes 💜 this icon of a manpage lives under ./include/linux, dated October 2026, and answers to the name kmap(9) — mwah, go map something responsibly 💅🎀

📦 where this page comes from